Observation of B+->Lambda_c+Lambda_c-K+ and B0->Lambda_c+Lambda_c^-K0 decays

We report first measurements of the doubly charmed baryonic B decays B->Lambda_c+Lambda_c-K. The B+->Lambda_c+Lambda_c-K+ decay is observed with a branching fraction of (6.5+1.0-0.9+-1.1+-3.4)x10^{-4} and a statistical significance of 15.4sigma. The B0->Lambda_c+Lambda_c-K0 decay is observed with a branching fraction of (7.9+2.9-2.3+-1.2+-4.2)x10^{-4} and a statistical significance of 6.6sigma. The branching fraction errors are statistical, systematic, and the error resulting from the uncertainty of Lambda_c+->pK-pi+ decay branching fraction. The analysis is based on 357fb-1 of data accumulated at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e- collider.Comment: 10 pages, 3 figure

Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle

The Collins effect connects transverse quark spin with a measurable azimuthal dependence in the yield of hadronic fragments around the quark's momentum vector. Using two different reconstruction methods we observe statistically significant azimuthal asymmetries for charged pion pairs in e+e- annihilation at a center-of-mass energy of 10.52 GeV, which can be attributed to a transverse polarization of the primordial quarks. The measurement was performed using a sample of 79 million hadronic events collected with the Belle detector.Comment: 6 pages, 4 figure

Measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar

We report on a measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar with 275 million BBbar events collected at the Upsilon(4S) resonance with the Belle detector at KEKB. Events are tagged by fully reconstructing one of the B mesons in hadronic modes. We obtain Br(B- --> D+ pi- l- nu-bar) = (0.54 +/- 0.07(stat) +/- 0.07(syst) +/- 0.06(BR)) x 10^-2, Br(B- --> D*+ pi- l- nu-bar) = (0.67 +/- 0.11(stat) +/- 0.09(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D0 pi+ l- nu-bar) = (0.33 +/- 0.06(stat) +/- 0.06(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D*0 pi+ l- nu-bar) = (0.65 +/- 0.12(stat) +/- 0.08(syst) +/- 0.05(BR)) x 10^-2, where the third error comes from the error on Bbar --> D(*) l- nu-bar decays. Contributions from B0bar --> D*+ l- nu-bar decays are excluded in the measurement of B0bar --> D0 pi+ l- nu-bar.Comment: 6 pages, 10 figures, submitted to Physical Review D (Rapid Communication), the Lepton-Photon 2005 Conference (Uppsala, Sweden) and the HEP2005 Europhysics Conference (Lisboa, Portugal

Measurement of the wrong-sign decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi-, and search for CP violation

Using 281 fb^-1 of data from the Belle experiment recorded at or near the Upsilon(4S) resonance, we have measured the rates of the ``wrong-sign'' decays D0 -> K+ pi- pi0 and D0 -> K+ pi- pi+ pi- relative to those of the Cabibbo-favored decays D0 -> K- pi+ pi0 and D0 -> K- pi+ pi+ pi-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D0bar mixing; the latter has not yet been observed. We obtain R_WS(Kpipi0)=[0.229 +/-0.017(stat.) +0.013-0.009(sys.)]% and R_WS(K3pi)=[0.320 +/-0.019(stat.) +0.018-0.013(sys.)]%. The CP asymmetries are measured to be -0.006 +/- 0.053 and -0.018 +/- 0.044 for the K+ pi- pi0 and K+ pi- pi+ pi- final states, respectively.Comment: 10 pages, 3 figures, submitted to PRL, Lepton-Photon 2005 Conference in Uppsala, Sweden and HEP2005 Europhysics Conference in Lisboa, Portuga

Improved Constraints on D0-D0bar Mixing in D0 -> K+ pi- Decays from the Belle Detector

We report the results of a search for D0-D0bar mixing in D0 -> K+ pi- decays based on 400 fb^{-1} of data accumulated by the Belle detector at KEKB. Both assuming CP conservation and allowing for CP violation, we fit the decay-time distribution for the mixing parameters x' and y', as well as for the parameter R_D, the ratio of doubly-Cabibbo-suppressed decays to Cabibbo-favored decays. The 95% confidence level region in the (x'^2,y') plane is obtained using a frequentist method. Assuming CP conservation, we find x'^2<0.72 x 10^{-3} and -9.9 x 10^{-3}<y'<6.8 x 10^{-3} at the 95% confidence level; these are the most stringent constraints on the mixing parameters to date. The no-mixing point (0,0) has a confidence level of 3.9%. Assuming no mixing, we measure R_D=(0.377+-0.008+-0.005)%.Comment: 6 pages, 3 figures, 1 table; replaced with the version of Phys. Rev. Let

Moments of the Hadronic Invariant Mass Spectrum in B --> X_c l nu Decays at Belle

We present a measurement of the hadronic invariant mass squared (M^2_X) spectrum in charmed semileptonic B meson decays B --> X_c l nu based on 140 fb^-1 of Belle data collected near the Y(4S) resonance. We determine the first, the second central and the second non-central moments of this spectrum for lepton energy thresholds ranging between 0.7 and 1.9 GeV. Full correlations between these measurements are evaluated.Comment: published version of the paper (one figure added, minor changes in the text); 16 pages, 3 figures, 10 table

Time-Dependent CP Asymmetries in B0 -> Ks pi0 gamma transitions

We report measurements of CP violation parameters in B0->Ks pi0 gamma transitions based on a data sample of 535x10^6 BB pairs collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. One neutral B meson is fully reconstructed in the B0->Ks pi0 gamma mode. The flavor of the accompanying B meson is identified from its decay products. For a Ks pi0 invariant mass up to 1.8 GeV/c^2, we obtain S = -0.10 +- 0.31 +- 0.07 and A = -0.20 +- 0.20 +- 0.06. For a Ks pi0 invariant mass near the K*0(892) resonance, we obtain S = -0.32 +0.36-0.33 +-0.05 and A=-0.20 +-0.24 +-0.05.Comment: 6 pages, 3 figures, accepted by PR

Study of B+- --> D_CP K+- and D^*_CP K+- decays

We report a study of the modes D_CP K+- and D^*_CP K+- where D^(*) decays to CP eigenstates. The data sample used contains 275 x 10^6 BB events at the Upsilon(4S) resonance collected by the Belle detector at the KEKB energy-asymmetric e^+ e^- collider. The CP asymmetries obtained for D_CP K are: A_1 = 0.06 +- 0.14 (stat) +- 0.05 (sys), A_2 = -0.12 +- 0.14 (stat) +- 0.05 (sys) and for D^*_CP K : A_1^* = -0.20 +- 0.22 (stat) +- 0.04 (sys), A_2^* = 0.13 +- 0.30 (stat) +- 0.08 (sys).Comment: 10 pages, 7 figures, submitted to Phys.Rev.D (Rapid Communications

Measurements of exclusive B_s^0 decays at the Y(5S) resonance

Several exclusive $B_s^0$ decays are studied using a 1.86 fb-1 data sample collected at the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. In the $B_s^0 \to D_s^- \pi^+$ decay mode we find 10 $B_s^0$ candidates and measure the corresponding branching fraction. Combining the B_s^0 -> D_s^{(*)-} \pi^+, B_s^0 -> D_s^{(*)-} \rho^+, B_s^0 -> J/\psi \phi and B_s^0 -> J/\psi \eta decay modes, a significant $B_s^0$ signal is observed. The ratio \sigma (e^+ e^- -> B_s^* \bar{B}_s^*) / \sigma (e^+ e^- -> B_s^{(*)} \bar{B}_s^{(*)}) = (93^{+7}_{-9} \pm 1)% is obtained at the Y(5S) energy, indicating that $B_s^0$ meson production proceeds predominantly through the creation of $B^*_s \bar{B}^*_s$ pairs. The $B_s^0$ and $B_s^*$ meson masses are measured to be M(B_s^0)=(5370 \pm 1 \pm 3)MeV/c^2 and M(B_s^*)=(5418 \pm 1 \pm 3)MeV/c^2. Upper limits on the B_s^0 -> \gamma \gamma, B_s^0 -> \phi \gamma, B_s^0 -> K^+ K^- and B_s^0 -> D_s^{(*)+} D_s^{(*)-} branching fractions are also reported.Comment: 9 pages, 5 figures, published in Phys. Rev. D76, 012002 (2007

Search for the b --> d gamma process

We report the results of a search for the flavor-changing neutral current process b --> d gamma using a sample of 275 million B meson pairs accumulated by the Belle detector at KEKB. We find no significant signal for the exclusive decays B- --> rho- gamma, B0B --> rho0 gamma, or B0B --> omega gamma. Assuming an isospin relation between the three modes, we set an upper limit for the combined branching fraction Br(B --> (rho,omega) gamma) < 1.4 x 10-6 at the 90% confidence level. This limit can be used to constrain the ratio of CKM matrix elements |Vtd/Vts|.Comment: 6 pages, 2 figures, submitted to Phys. Rev. D (RC